Beardsley, J.W.

Hapai, J.M.

McEwen, F.L.

Su, T.H.

Proceedings of the Hawaiian Entomological Society

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Vol. XIII, No. 1, April 1979 119Laboratory Tests with Candidate Insecticidesfor Control of the Big-Headed Ant, Pheidolemegacephala (Fabricius)1F.L. McEwen, J.W. Beardsley, Jr. M. Hapai and T.H. SuDEPARTMENT OF ENTOMOLOGY, COLLEGE OF TROPICAL AGRICULTUREUNIVERSITY OF HAWAII, HONOLULU, HAWAIIThe big-headed ant, Pheidole megacephala (Fabr.) is the dominant ant speciesin pineapple fields in Hawaii (Phillips, 1934). Its main importance is the role it playsin nursing mealybugs; in particular the gray mealybug, Dysmicoccus neobrevipesBeardsley, the principal vector of mealybug wilt to pineapple. According to Carter(1967) the ant is essential to the well-being of the mealybug in that it ''fights offpredators and parasites, cleans up the masses of honeydew secreted by themealybugs and eats dead and dying members of the colony." Carter (1967) pointedout further that the ants move mealybugs from one plant to another and that in theabsence of ants, "mealybug infestations either die out or are very small in numbers."Prior to 1945, ant control in pineapple plantations was difficult to achieve, theonly methods available being the use of ant fences and long intercycles betweenplantings. Mealybugs were abundant and pineapple wilt a serious factor in production. When DDT became available it was found that this insecticide provided control of the big-headed ant and the practice was adopted of using a broadcast spray of4 lbs. active per acre as soon as possible after the pineapples were planted followedby three more applications of 2 lbs. active per acre at monthly intervals. In fieldswhere excessive trash was present, the ants were more difficult to control and DDTat 10 lbs. per acre was sometimes applied to the standing ratoon field prior toknockdown.When the cyclodine insecticides became available these proved to be better for-micides than DDT, and heptachlor was used at 3 lbs. active per acre as a pre-planting treatment followed by 1 or 2 lbs. active per acre, annually, to the growingcrop (Carter, 1967).Efforts toward developing inexpensive and effective methods to control the imported fire ants, Solenopsis richteri Forel and S. invicta Buren, concentrated onbaits and chlordecone (Kepone®) was found effective when incorporated in avariety of baits (Hays and Arant, 1960; Bartlett and Lofgren, 1961). A closely related compound Mirex® was found more effective (Lofgren et al., 1962) and experiments showed that among others, soybean oil was highly attractive to the ants andthat corn cob grits were a most practical carrier (Lofgren et al., 1963). Later studiesconfirmed the superiority of Mirex® (Stringer et al., 1964) and a Mirex® bait usingsoybean oil as the attractant and corn cob grits as the carrier came into general usefor control of the imported fire ants. This represented a major development inefficient use of pesticides.1 Published with the approval of the Director of the Hawaii Agricultural Experiment Station as JournalSeries No. 2171.120 Proceedings, Hawaiian Entomological SocietyThe Mirex® bait (3,000 ppm Mirex®) was found effective in controlling ants inpineapple plantings when used at about 2.5 lb. bait per acre (Sakimura, 1970) andaerial applications of this bait was adopted by some plantations as the method ofcontrol for the big-headed ant. Some plantations, however, continued to use thebroadcast treatments with heptachlor. As a result of the availability of these materials, plantations have achieved excellent control of ants; mealybugs are seldomfound in large numbers and mealybug wilt has virtually disappeared.DDT, heptachlor and Mirex® are each persistent insecticides, only slowly degraded in nature. As a result, residues of these compounds or their breakdownproducts have appeared in many non-target organisms, sometimes with deleteriouseffects (Edwards, 1973). Thus, in the United States, DDT has been banned for useon agricultural crops and heptachlor and Mirex® currently are under review.Mirex® bait may not be applied by air after December 31, 1977 (O'Neil, 1976).Since the pineapple industry must have effective methods of ant control toensure that the devastating wilt disease does not reappear, a number of insecticideswere evaluated for their potential as formicides against the big-headed ant. Emphasis was placed on bait preparations since baits offer the most efficient use ofinsecticides and have the added advantage of providing a degree of selectivity sinceonly those animals attracted to the baits will be exposed in a major way to effects ofthe pesticide.Materials and MethodsBaits were prepared using corn grits with 15% soybean oil as used in the commercial Mirex® baits (Fancher, personal communication). In most cases the insecticide formulation tested would dissolve in the soybean oil. Where the formulationdid not disperse well in the oil, the corn grits were treated with the appropriateamount of oil and the insecticide added in a water suspension. Baits were preparedof 1000, 100, 10, 1 and 0.1 ppm with each insecticide.After the baits were prepared they were tested in two ways.1. Toxicity to the big-headed ant. For this test, about 1 gram of bait was placed inthe bottom of a 10 dram plastic vial. Four vials were utilized for each dosage rate ofeach chemical tested. A small piece (4 mm3) of a honey agar (100 ml H2O; 13 mlhoney; 1 gm agar) was added to each vial to provide water and nourishment for theants. Worker ants were collected by placing bait (the honey agar described above) ina Petri dish near the base of a kiawe tree where ants were abundant and after collection these weie placed, 10 per vial, in the vials containing experimental baits. Thevials were capped (snap-on plastic tops) and retained in an upright position for 48hours. Mortality was determined after 24 and 48 hours.2. Attractancy of baits. About 3 grams of each bait were placed in an 8 ozplastic-lined paper hot food container and covered with a plastic lid. A hole approximately lcm2 was made in either side, mid-way up on the container and the container was placed in an area known to be infested heavily with the big-headed ant.Four containers were used for each bait tested and counts were made of the numberof ants (workers and soldiers) attracted inside each container. The containers wereplaced on the ground in the infested area between 3:00 and 4:00 PM and readingswere made at dusk, about 7:00 PM.Two insecticides were tested each day and a set offour check vials, each containing the bait of corn grit plus soybean oil, was included with each day's testing.Vol. XIII, No. 1, April 1979 121Check containers were included also in the attractancy tests and for these the containers were randomly distributed about 30 cm apart since ant activity in the areawas not uniform.ResultsIn most cases mortality in the check vials was low, if the soybean oil was increased beyond 15%, mortality increased, the ants seeming to become coated withthe oil. In the bait attractancy tests, each of the check containers normally attracted50 to 100 ants. Data on percentage mortality after 24 and 48 hours and attractancy(expressed as a percentage of the check) are presented in Table 1.The candidate insecticides tested included a number known to have activityagainst ants and others of unknown potential. In the toxicity tests, the proceduredid not differentiate among contact, ingestion or vapor toxicity and results thusindicate maximum toxicity. Under this regime many of the insecticides werehighly toxic, some giving almost complete mortality in 24 hours at dosages as lowas 1 ppm. With some insecticides there were differences between formulations.With diazinon for example, the technical and emulsifiable formulations were moretoxic than the wettable powder or the microencapsulted and with fonofos and N2596, the technical material appeared more toxic than the emulsifiable. With a fewinsecticides, notably dichlorvos, naled and bendiocarb, mortality was extremelyrapid but with most materials there was an increase in mortality (where 100% mortality did not occur in 24 hrs.) between the 24 hr. and 48 hr. counts.In the attractancy tests, only Mirex® and Vendex® baits, attracted at the 1000ppm level. Attractancy of the baits increased as the concentration of toxicants decreased but some repellency of the toxicants was evident even at 0.1 ppm.DiscussionIn their studies on baits for the imported fire ant, Stringer etal. (1964) suggestedthat effective toxicants for inclusion in the baits should exhibit delayed toxicityover a wide range of dosages, be transferred readily from one ant to another, andnot be repellent to the ants. In earlier tests only chlordecone and Mirex® met thesequalifications and despite extensive screening of compounds (Lofgren etal., 1967)other toxicants effective against the imported fire ant have not been found. In ourtests those insecticides that were highly toxic to the ants were repellent in baits atdosages needed for control.It is accepted generally that every effort should be made to replace non-biodegradable pesticides with those that break down readily in nature (Nat. Acad.Sci., 1975). While this concept has much merit, the requirements in control maymake such a concept unrealistic in some situations. Control of some social insectsis one such circumstance.The effectiveness of Mirex® ant bait derives from two characteristics of the insecticide additional to its toxicity. It is not repellent to ants (at low concentrations)and it is not broken down readily in the insect digestive tract. Thus the insecticideremains active in the communal stomach of the ant colony and the regurgitatednourishment passed from one ant to another serves as the vehicle for distribution ofthe insecticide within the colony. Stringeret al. (1964) considered this essential foran effective toxicant for ant baits, but this kind of activity is not usually characteristic of a biodegradable insecticide.122 Proceedings, Hawaiian Entomological SocietyMirex® ant bait is used in pineapple production once each year at a dosage of 2.7grams active chemical per acre. Under somewhat similar application dossages,large-scale applications of Mirex® bait for control of the imported fire ants in thesouthern United States resulted in detectable residues in some non-target animalspecies (Wolfe and Norment, 1973; Baetche et al., 1972; Markin et al., 1974),more notable in aquatic areas. In all cases residues were extremely low and unlikelyto have any significance to the organism. Since this is the case, it would seem that inthe absence of suitable alternative insecticides for ant baits, a strong case can bemade for retaining Mirex® for discretionary usage. Control of ants in pineappleplantations would appear to be the kind of discretionary use acceptable, sincepineapple fields are recycled to pineapple and other cropping or grazing is not practised. Care in application should be exercised so that waterways are not treated inadvertently. Mirex® does eventually break down in the environment (Carlson et al.,1976) and with the facts in hand, it seems inconceivable that 2.7 grams of Mirex®per acre represents a greater environmental hazard than would an alternative antcontrol program using a broadcast application of pesticide in which up to severalhundred times this amount of toxicant is required.References CitedBaetche, K. P., J. Cain, and W. E. Poe. 1972. Mirex and DDT residues in wildlife and miscellaneoussamples in Mississippi—1970. Pest. Monitor. Jour. 6: 14-22.Bartlett, F. J., and C. S. Lofgren. 1961. Field studies with baits against Solenopsis saevissima v.richteri, the imported fire ant. J. Econ. Entomol. 54: 70-73.Carlson, D. A., K. D. Konyha, W. B. Wheeler, G. P. Marshall, and R. G. Zaylskie. 1976. Mirex in theenvironment: its degradation to kepone and related compounds. Sic. 194: 939-941.Carter, W. C. 1967. Insects and related pests of pineapple in Hawaii. Pineapple Research Institute (Restricted publication).Edwards, C. A. 1973. Environmental pollution by pesticides. Plenum Press, London and N. Y. pp. 542.Hays, S., and F. S. Arant. 1960. Insecticide baits for control of the imported fire ant, Solenopsis saevissima reichteri. J. Econ. Entomol. 53: 188-191.Lofgren, C. S., C. E. Stringer, and F. J. Bartlett. 1962. Imported fire ant toxic bait studies: GC-1283, apromising toxicant. J. Econ. Entomol. 55: 405-407.Lofgren, C. S., F. J. Bartlett, and C. E. Stringer. 1963. Imported fire ant toxic bait studies: evaluation ofcarriers for oil baits. J. Econ. Entomol. 56: 62-66.Lofgren, C. S., C. E. Stringer, W. A. Banks, and P. M. Bishop. 1967. Laboratory tests with candidatebait toxicants against the imported fire ant. U.S.D.A. Agr. Res. Serv. ARS 81-14. pp. 25.Markin, G. P., H. L. Collins, and J. Davis. 1974. Residues of the insecticide Mirex in terrestrial andaquatic invertebrates following a single aerial application of Mirex bait, Louisiana—1971-72. Pest.Monitor. Jour. 8: 131-134.National Academy of Sciences. 1975. Contemporary pest control practices and prospects. Vol. I. Nat.Acad. Sci., Wash. D. C. pp. 506.O'Neill, 1976. Train accepts Mississippi plan to end Mirex use against fire ants. Environmental News.EPA. Oct. 21.Phillips, J. S. 1934. The biology and distribution of ants in Hawaiian pineapple fields. Univ. HawaiiExp. Sta. Pineapple Producers' Cooperative Assoc. Ltd. Bull. 15.Sakimura, K. 1970. Mirex applied by airplane for ant control. Pineapple Research Institute News 18:1-4(Restricted Publication).Stringer, C. E., C. S. Lofgren, and F. J. Bartlett. 1964. Imported fire ant toxic bait studies: evaluation oftoxicants. J. Econ. Entomol. 57: 941-945.Wolfe, J. L., and B. R. Norment. 1973. Accumulation of Mirex residues in selected organisms after anaerial treatment, Mississippi—1971-72. Pest. Monitor. Jour. 7: 112-116.Table 1. 24 hour and 48 hour mortality and attractancy of corn cob-soybean oil baits to Pheidole megacephalaInsecticideBendiocarb.CarbarylCarbofuranCholobenzilateChlordaneChlorpyrifosChlorpyrifosDiazinonDiazinonDiazinonDiazinonDichlorvosDimethoateDisystonFonofosFonofosHeptachlorMethamidophosMethidathionMethidathionMethomylMirexNaledNemacurOrthene®Orthene®PhosalonePropoxurTrichlorfonVendexCGA 12223/3N-2596/4N-2596/4Formulation76% W.P.50% W. P.4.8F45% W.P.Tech.41% E.C.Tech.Ag 500 E.C.Mic. 23% E.C.50% W.P.Tech.Tech.2 E.C.Tech.4 E.C.Tech. 93%Tech.40 E.C.Tech.79.4% E.C.90% sp.Tech.8 E.C.Tech.75% W.P.15.6% E.C.25% W. P.Tech.80% sp.50% W.P.13.5% E.C.4 E.C.Tech.10001001001002.510010010010010010010010010010010010010010010010097.59510097.597.510052.510040010010010024 hr.100100451002.587.5508010087.590100100951009010010010097.597.5104092.53592.567.515100152.5100100100mortality % atppm in1010037.552.522.517.51582.5522.58510055952.51001007542.572.52522.585107522.537.510152.510025100bait1.09027.5501002.582.52.5047.587.516.562.52.592.545252.517.5517.5752.527.53517.52.512.52.597.52.587.5V0.13012.52.52.5002.51552.52.58057.57.5101012.52.527.557.53512.57.52.53010557.55450.0512.50.00005502.5547.501002.50100152.52.51.5100012.5102.52.55102.510001001001002.510010010010010010010010010010010010010010010010010010010010010010055100705100100100100100551007.510010010010010010010010010010097.510010010097.510032.597.51006010097.53010037.5510010010048 hr. mortality at Vppm in bait101005512.52.510042.592.51004042.510010092.510027.510010010082.597.57.537.51004092.560401532.55100901001.0903552.5657.582.51001017.575100601002.510010062.51087.5517.587.52.537.547.532.57.522.57.510027.51000.135252.52.52.551552.557.52510012.52512.547.577.5655557.510701012.52.532.57.555152597.50.012.525502.555152.52.522.572.52.517.52.57.52.522.5057.552.557.512.5002512.52.5522.517.57.5100022520122110001311911010601032603757025Attractancy -%100321313196102821313154237501301520112771062420265ppm102212771213120597385305010102346622168114141248485121375715713of checkin bait21.03192710050141857767909334121581785034115230681342627598156521367650.1384159136113857797109145654111129958134268011766716756105703562130112105129 (III,f>V 10 worker ants placed in each of 5 vials containing about 1 gm. of bait and an agar food supply.21 Based on number of ants attracted to 8 oz. food containers containing about 3 gr. bait. Four containers for each bait. Check bait-corn cob with 10% soybean oil.3/ 0-(5-Chloro-l [methylethylJ-lH-1, 2, 4-triazol-3yl) 0, 0-diethyl phosphorthioate.41 O-ethyl S-(p-chlorophenyl) ethylphosphonodithioate.124 Proceedings, Hawaiian Entomological Society

Laboratory Tests with Candidate Insecticides for Control of the Big-Headed Ant, Pheidole megacephala (Fabricius)

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Laboratory Tests with Candidate Insecticides for Control of the Big-Headed Ant, Pheidole megacephala (Fabricius)

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